Sequential Diffusion Spectra as a Tool for Studying Time-Dependent Translational Molecular Dynamics: A Cement Hydration Study

Abstract

The translational molecular dynamics in porous materials are affected by the presence of the porous structure that presents an obstacle for diffusing molecules in longer time scales, but not as much in shorter time scales. The characteristic time scales have equivalent frequency ranges of molecular dynamics, where longer time scales correspond to lower frequencies while the shorter time scales correspond to higher frequencies of molecular dynamics. In this study, a novel method for direct measurement of diffusion at a given frequency of translational molecular dynamics is exploited to measure the diffusion spectra, i.e., distribution of diffusion in a wide range of frequencies. This method utilizes NMR modulated gradient spin-echo (MGSE) pulse sequence to measure the signal attenuation during the train of spin-echoes formed in the presence of a constant gradient. From attenuation, the diffusion coefficient at the frequency equal to the inverse double inter-echo time is calculated. The method was employed to study the white cement hydration process by the sequential acquisition of the diffusion spectra. The measured spectra were also analyzed by the diffusion spectra model to obtain the time-dependence of the best-fit model parameters. The presented method can also be applied to study other similar systems with the time evolution of porous structure.

Comparing CT and MR Properties of Artificial Thrombi According to Their Composition

“…The temporal parameter ∆, also known as the diffusion time, can have a great influence on the diffusion measurement of a porous system. For a porous system with pore diameter a, the measured diffusion coefficient would be equal to the unrestricted diffusion coefficient D 0 when ∆ a 2 /6D 0 , and it would decrease and level off to D ∞ when ∆ a 2 /6D 0 , where the ratio D 0 /D ∞ is equal to the tortuosity of the porous medium [28,29]. For ∆ values between these two extremes, the measured diffusion coefficient is between D ∞ and D 0 , and its value depends on the ratio of ∆ to a 2 /6D 0 .…”

A Simple Cement Hydration Model Considering the Influences of Water-to-Cement Ratio and Mineral Composition

“…In recent years, many new technologies and methods are used [17][18][19][20][21][22][23][24][25][26][27][28]. The Avrami equation [10] is used in some investigations [12,17] to assess the rates of the four dominant compounds in Portland cement, C 3 S, C 2 S, C 3 A, and C 4 AF.…”